Recently, as a portion of an engine control for improving the feeling of running and the fuel economy of an automobile, a throttle valve control by means of an electronic controlled actuator which does not use any mechanical linkage between a throttle valve and an acceleration pedal and controls an opening of the throttle valve in response to an electric signal obtained by converting an amount of depression of an acceleration pedal and other signals such as engine rotation signal which is representative of engine operating condition and gear position signal which is representative of automobile running condition has been developed.
In the throttle valve control device using such electronic controlled actuator, the throttle valve opening is regulated by a driving motor actuated upon instructions from an automobile control device comprising an operation control portion for sequentially operating an optimum throttle opening according to signals representative of an engine operating condition and automobile running condition. Therefore, it is necessary to have a safety device capable of preventing an uncontrolled running of the automobile even if the electronic controlled actuator becomes inoperative during running of the automobile, and examples of such safety device are shown in Japanese Patent Application Laidopen No. 145867/1980 as
(1) provision of a return spring on a throttle shaft which functions to return a throttle valve to a closed position when a control is lost,
(2) provision of an electromagnetic clutch for disconnecting a throttle shaft from an electronic controlled actuator when it becomes uncontrollable, or
(3) provision of a construction which is a combination of a return spring and an electromagnetic clutch and functions to make the return spring effective when the electromagnetic clutch is separated.
In the conventional schemes such as above, however, once the electronic controlled actuator becomes inoperative, it is impossible to maintain a running of an automobile and thus it becomes impossible to move the automobile to a repairing place, although it is possible to prevent an uncontrolled running of the automobile.
The present invention was made in view of solving this problem and an object of the present invention is to provide a throttle valve control device which is highly reliable and has a high speed response.